1. Field of the Invention
The present invention pertains to the art of refrigerators and, more particularly, a refrigerator assembly incorporating a Stirling cycle refrigeration system, the operating phase of which can be electronically controlled to effect both cooling and defrosting of a freezer compartment of the refrigerator.
2. Discussion of the Prior Art
The Stirling cycle is a known type of efficient refrigeration cycle. Such a cycle functions by directing a working fluid through four repetitive operations, i.e., a heat addition operation at constant temperature, a constant volume heat rejection operation, a constant temperature heat rejection operation and a heat addition operation at constant volume. It has been previously proposed to utilize a Stirling cycle in a refrigeration system, particularly a heat pump system. However, it has also been proposed in the art to utilize a Stirling cycle for use in a refrigerator. Such a Stirling cycle arrangement would incorporate an expander having an associated expansion space piston and a pulsator which has an associated compression space piston. In a conventional Stirling cycle refrigeration system, the phase relationship between the expansion piston and the compression piston is determined by a mechanical coupling between the pistons. However, particularly in view of the desire to adjust the degree of refrigeration, it has also been proposed to electronically control the time phase relationship between the expansion and compression pistons in order to alter the cooling capacity of the overall system. That is, the phase relationship can be altered, such as by changing the driving frequency for the expander and compressor, in order to actually reduce the maximum cooling capacity.
Despite these advances, the use of Stirling cycle refrigeration systems has not been widely accepted, in part due to the fact that the electronic controls proposed for such Stirling cycle systems do not provide for all of the cycles incorporated in more conventional refrigeration systems. For instance, the prior art dealing with Stirling cycle refrigeration systems have not addressed providing an automatic defrosting operation. For this and other reasons, there exists a need in the art for an improved refrigerator incorporating a Stirling cycle refrigeration system which can be electronically controlled to perform multiple operations, including both cooling and defrost operations, automatically. In addition, there is need in the art for a compact Stirling cycle system for use in a refrigerator.